In typical cellular wireless communication systems, wireless communication devices (e.g., cell phones, personal digital assistants, laptops, netbooks, tablets, and/or other wirelessly equipped devices, any of which may be referred to as a user equipment device (UE) for brevity) subscribe to service from a given cellular wireless service provider. In practice, a service provider will operate one or more networks (sometimes referred to as radio access networks (RANs)) including base stations that radiate to define one or more wireless coverage areas, referred to as sectors, where the subscriber UEs can operate.
Generally, wireless communications between a given UE and a serving base station in a RAN are carried out in accordance with one or more air interface protocols such as Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Operability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), GSM, GPRS, UMTS, EDGE, DEN, TDMA, AMPS, MMDS, WIFI, and BLUETOOTH, or others now known or later developed. Through each base station (and corresponding RAN), a UE can obtain connectivity to other networks such as the public switched telephone network (PTSN) and the Internet. In addition to base stations, each RAN may include one or more radio network controllers (RNCs), or the like, which may be integrated with or otherwise in communication with the base stations, and which may include or be in communication with a switch or gateway that provides connectivity with one or more transport networks. Conveniently with this arrangement, a UE that is positioned within coverage of the RAN may communicate with a base station and in turn, via the base station, with other served devices or with other entities on the transport network.
In general, each base station in a RAN may be configured to operate on one or more frequency bands and, in each such band, to provide service on one or more frequency channels. Example frequency bands, each defining a particular range of radio frequency spectrum, include the 800 MHz band, the 1.9 GHz band, and the 2.5 GHz band. Each frequency channel within a band may then be arranged as a specific block of frequency, such as a 1.25 MHz block, a 5 MHz block, a 10 MHz block, or the like. Further, in certain systems, each frequency channel may include one block of frequency for downlink communications from the RAN to UEs and a corresponding but separate block of frequency for uplink communications from UEs to the RAN. Whereas, in other systems, each frequency channel may be divided over time to separately carry downlink and uplink communications.
To enable UEs to select coverage areas in which to operate, each base station may also be configured to broadcast a specification of the one or more frequency channels on which it operates and to broadcast on each such frequency channel one or more pilot or reference signals that UEs are configured to monitor in order to evaluate coverage strength (e.g., signal strength and/or signal to noise ratio). For example, in a representative LTE system, each base station broadcasts on each of its one or more frequency channels a system information block (SIB) message that lists the frequency channels on which the base station provides service, and each base station further broadcasts on each listed frequency channel a reference signal that LTE-compliant UEs are arranged to monitor in order to evaluate LTE coverage provided by the base station. Similarly, in a representative CDMA system, each base station broadcasts on each of its one or more frequency channels a channel list message (CLM) that lists the frequency channels on which the base station provides service, and each base station further broadcasts on each listed frequency channel a pilot signal that CDMA-compliant UEs are arranged to monitor in order to evaluate CDMA coverage provided by the base station.
When a UE first enters into coverage of a RAN, the UE may automatically scan the airwaves in an effort to find the strongest available coverage, and the UE may then register with the RAN. For instance, the UE may generally scan through various frequency channels and evaluate any reference signals on those frequency channels, and the UE may determine which reference signal is the strongest, thereby identifying an optimal frequency channel and base station coverage area. The UE may then engage in registration signaling with the RAN on that frequency channel in that base station coverage area, to register with the RAN.
Once a UE is registered with a RAN in a particular coverage area, the UE may then be served by the RAN in that coverage area in an “idle” mode in which the UE regularly scans for page messages and other overhead information from the RAN. Further, the UE may engage in additional signaling with the RAN in order to be served by the RAN in an “active” or “connected” mode in which the UE may then engage in bearer communication, such as voice and/or packet-data communication with other entities as discussed above.